The term Diamond Like Carbon (DLC) describes a group of materials comprising carbon with structures and properties resembling that of diamond. Some examples of Diamond Like Carbon coatings are a-C, a-C:H, i-C, ta-C and ta-C:H coatings.
As DLC has many attractive properties including high hardness, chemical inertness, high thermal conductivity, good electrical and optical properties, biocompatibility and excellent tribological behavior, DLC has attracted a considerable interest as coating material.
A rough classification of DLC coatings is given by the fractions of sp3 bonding. Tetrahedral carbon coatings have a high fraction of sp3 bonded carbon, whereas amorphous carbon such as a-C or a-C:H coatings have a lower fraction of sp3 bonding and a higher fraction of sp2 bonding.
A second classification is given by the hydrogen content. The DLC coatings can be classified in non-hydrogenated coatings (ta-C and a-C) and hydrogenated coatings (ta-C:H and a-C:H).
The group of tetrahedral carbon coatings shows many interesting properties like a high hardness (resembling the hardness of diamond) and a high Young's modulus. These properties make tetrahedral carbon coatings ideal for many challenging wear-resistant applications. However, as the compressive stress is proportional to the sp3 bonding, the compressive stress in tetrahedral carbon coatings is high.
The large compressive stress in the coating limits the adhesion of the coating to the substrate and limits the overall film thickness of the coating.